Graded spin-on organic bottom antireflective coating for high NA lithography

Abstract

Immersion lithography for the 32nm node and beyond requires advanced methods to control 193 nm radiation reflected at the resist/BARC interface, due to the high incident angles that are verified under high numerical aperture (NA) imaging conditions. Swing curve effects are exacerbated in the high NA regime, especially when highly reflective substrates are used, and lead to critical dimension (CD) control problems. BARC reflectivity control is also particularly critical when underlying surface topography is present in buried layers due to potential reflective notching problems. In this work, a graded spin-on organic BARC was developed to enable appropriate reflectivity control under those conditions. The graded BARC consists of two optically distinct polymers that are completely miscible in the casting solution. Upon film coating and post-apply baking, the two polymers vertically phase-separate to form an optically graded layer. Different characterization techniques have been applied to the study of the distribution of graded BARC components to reveal the internal and surface composition of the optically graded film, which includes Variable Angle Spectroscopic Ellipsometry (VASE) and Secondary Ion Mass Spectroscopy (SIMS). Also, optical constant optimization, substrate compatibility, patterning defectivity and etch feasibility for graded BARC layers are described. Superior 193 nm lithographic performance and reflectivity control of graded BARC beyond 1.20 NA compared to conventional BARCs is also demonstrated.